Apparatus for and method of operating rectifying load devices



Dec. 6, 1932. w, KEARSLEY 1,890,330

APPARATUS FOR AND METHOD OF OPERATING RECTIFYING LOAD DEVICES ,Filed Feb. 6, 1930 Inventor:

\ L \X/LHLam K.l' ear-s le g, f v 1 MW HLs Attohne g.

Patented Dec. 6, 1932 E JST S A NT OEHCE WILLIAM K. KEnRsLEY, or scHENEcrAnY, imw YORK, ASSIGNOR To EnERAL ELECTRIC COMPANY, A CORPORATION OENEW YORK I APPARATUS ronanniin'rnon or ,ornjan'rms ancriiiyrne nnvrcns Application filed February 6,1830. I Serial No. 426,427:

The present invention relates to alternating current, apparatus containing a transformer and a load devlce, such as an X-ray tube,

which is unilaterally conducting, or reoti-' e 7.

It is the object of my invention to provide means for so operating such a trans former and. rectifying load that the high open-circuit or inverse voltage which tends To to occur during the halfv wave intervals when the load is non-conductive to current is materially reduced.

In accordance with my invention I have provided-a system wherein a unilateral load 1'5 device which, is operatively connected toan electromagnetic supply source, such. as a transformer, is combined with means whereby the flow of magnetizing current in the primary circuit of such-source is prevented 320 during the half wave intervals'when no 'current is flowing through the load device be cause of its rectifying character. 7 My invention will be more fully under stood by reference to the accompanying'speci- 2 flea-tion taken in connection with the accom panying drawing in which Fig. l-represents an X-ray system embodying my invention and containing an incandescent cathode X-ray device; Fig.2 illustrates a modifica tion in which the rectifying device in. the

primary circuit of the transformer acts also asa switch for controlling the flow of cur rent in the system; and Flg; 3 is a graph showing the relation of current to voltage in the primary circuit of the transformer.

Referring to Fig. 1, the system described comprises a transformer having as usual a magnetic core 1, a primary circuit 2and a secondary circuit 8. The transformer illusl '40 trated is of the step-up type, that is, has a low voltage primary and a high voltage secondary, having agreaten number of turns than the primary. Connected to the secondary conductors 4,5 is an X-raytube 6 ofthe well known form known as the Coolidge tube. Briefly, such an X ray tube comprises a highly evacuated bulb in which are sealed electrodes comprising a cathode '7 and anode 8. The cathode comprises a filament (not shown) connected by conductors 9, 10 to a source of current, whereby the filament may i i be heated tofincandescence, as representedbyl the low voltage secondary of a transformer. 11. The filamentary cathode issurrounded by afocusing cup 12 whereby,.a'thermionic I discharge from the filament is caused to be, focused and directed upon a target of' refrac tory metal 13 which is embedded in the'anode- 8. The main portion of the anode 8 and the anode stem 14: consists of a' metal of high heat conductivity, such as-copper, whereby theheat maybe carried away to an external radiator from thetarget 13 during operation;

An X-ray' tube such as described'is conductive to current only incne direction or polarity,

called useful half-wave impulseswhenthe polarity of the current waves onthe second? ary circuit are such asto' cause the flow" of electron current through the X-ray tube, and 1 also during the-opposite half wave impulsesi so During thelopposite half waves whenjho current flowsin the X-ray tube ahigh voltage is generated in the secondary circuit of the transformer and is impressed'upon the I X-rav tube through the conductors land .5.

The voltage during this periodof no current 7 flow. iscommonly calledthe inverse voltage. c This inverse Voltage is always higher than the useful voltage during thefperiodsof current-flow and. the greater the current "drawn by the X-ray tube the greater the difference between the useful voltage and the inversevoltage. It is undesirable that the X-ray tube should be subjected to higher voltage strains duri ig the inverse half wave inter ct vals than are" required for the" production of X-r'ays duringthe intervals ofuseful current i v flowt'hrough the X-ray tube. ,A'high in v ers'evoltage may cause electrical breakdown f j or the X-raytube'or the transformer.

, i In accordance with my invention a rectifier 1 18 is provided in the primary circuitof the transformer- 1. The particular rectifier illustrated in Fig. 1 is of the thermionic type and comprises'a sealed envelope containing a cath- I code 19, which is adapted to be maintained atv incandenscence bya separatefiow of current therethrough, and'thus being adapted to func- V tion as a source of electrons. The anode 20 com'monly consists of a plate, ormass of metal which is adapted to remain relatively I "cool during the operation of the rectifier, that is, below'the temperature at which appreciable electron emission can occur. I The env velope preferably shouldv contain a filllng of" monatomicgas,such as argon or other rare Y gas=or mercu'ryvapor. ,A drop o f'mercury in the evacuated envelope is indicated at 27.

In the case of mercury vapor the usual pressure is'within the limits of about 5vto 50 mi 'crons of mercury. Higher pressures may be i used in some cases. In place of the hotcathode jtype, ofrectifier illustrated in Fig. 1 other wel'lknown forms of valve devices, such i ye . i v I Fig. 1 shows the 'cathodef19 connected to as a mercury cathodearcrectifier, may be em the low voltage secondary of the transformer".

; '21 whereby'thecathode maybe maintained at f so incandescence. .The primaries of both the cathode heating transformers 11 and 21 are I 'connected respectively by the conductors 22 and '23 to altern atinge current; supply I mains '24 24. The anode 20 01 the rectifier lS is connected' to the supply conductor 16 ofthe transformer 1, the supply circuit for the transiformer l being completed through the conductor 25 to the mains 24, 2 1; A hand oper ated switch for the .circuit 25, has been diagrammatically indicated at 26. By the uni- V lateral conducting property ofthe rectifier 18's'ufficientlyhigh impedance is introduced into the circuit 17 during the periods of, inactivity of the X-ray tube to prevent theflow of magnetizing current through the primary; circuit 2. of the transformer 1 during, these: periods, thereby reducing the inverse voltage {impressed on the X-ray tube 6. i

i In; Fig. 3the flow of currentduring alternatinghalffwave impulses; in the primary circuit '2 is" represented bythe current wave j During the flow of load current through the rectifier in the primary circuit 16,17 of the transformer a current of opposite'polarthroughthe X-ray tube. The primaryvolt- Qage of this useful current is representedfby the curve 31; thejsecondary'vol'tage is,,not shown. When the polarity in the primary circuit rever'ses, thefhalf wave of current which. would flow except for thepresenceof l therectifier is suppressedifSome inverse voltage is still impressed by the transformer upon max-my tube d'uring this period of no current-V in: primary circuitdue to the collapse of the magnetic field of the-core of the transformer. vHowever, this inverse voltage, the primary counterpart which is represented by the curve 32,iis very much lower than an inverse voltage produc'e'dby a flow of magnetizing current through theprimary of the transforn'ier. The curve 33',

shown in dotted lines, represents visually the high inverse voltage which would occur if the rectifier 18 were not present; ,It will be observed that the peakfof the inverse voltage32 is less than the peak of the useful volts age 31. If" the rectifier "were not present the 7 peak of inverse voltage would .be materially higherthan the peakof the useful voltage-v 31 as indicated. For example, in the case of 'an X-ray outfit operating with a useful voltage of eighty-five thousandvolts'anda current of thirty mil'liamperes, such undesired inverse voltage may be seven thousand volts. higher than 'theuseful voltage, thus; come if spondmgly endangering the X-ray tube and V 1 i transformer. In a system containing arectifier as described above about eighty milliam peres can be drawn bythe X-ray tube with milliamperes are drawn without it In the system illustrated in Fig. 2 therectifier in the primary circuit "16, 17 iris reps resented by athree element gaseous discharge device 35. In addition'to an incandescent cath0de'19 and an anode 20 this device also has a gridor' control electrodei' 36. .Afdis-l charge device of-this character is described j in an a ticle by'Dr. .AQ' /V. Hull published in the- General Eiectric Review, vol.g32, (1929),,pages 312-323 incl. an pages 390;.

399 incl. article, current flow through the gas-filled thermionic device is prevented when theigri'd AS described by'Dr, Hull in this; i

electrode 36 is negativelycharged with [respect to the cathode. Means for producing I thereby the; control electrode-36 is connected flowloccurs through the rectifier and the 'X ray tube is energizedas' above 'des'eribed.

Current flow, however, can occur only dur ing the half wave impulses when the X ra'y tube 6 is cionductingzload current; During K the opposite half waveimpulses thefiowbf magnetizing current through the transformer is prevented as described in. accordance with Fig. 1. scone pressure is released from the spring' o'perated switch jilgfthecontrol L electrode becomes negative and stopst-he fiow e i v offcurrent'through the rectifier at the next ,zero po1nt. of current wave I gizing the transformerf' ;f j p r i even less inverse voltage than when V-thirty at v ' transformer having a primary and a seconda ductive.

An X-ray outfit in which the inverse voltage rose to a permissible maximum value with an observed non-rectified primary cur- -rent input, could be operated in accordance with my invention with a rectified primary current input of three times the observed value of this non-rectified primary current,

crating and to preventcurrent flow during intervals of opposite potential when saidX ray tube is non-operative. v In witness whereof, I have my hand this 5th day of February 1930.

- WILLIAM K. KEARSLEY.

without exceeding the permissible maximum :inverse voltage. 7 What I claim as new and desire to secure by Letters Patent of the United States, is:

1. An alternating current system comprising a transformer having primary and sec ondary circuits, a unilaterally conducting load, device in a secondary circuit, and valve means in a primary circuit constructed and connected to conduct current continuously in :said circuit during the half wave intervals of useful current flow in said load device and preventing flow of a magnetizing current in said primary circuit during the half wave intervals when said device is non-con- 2. An X-ray system comprising a transformer, a rectifying X-ray' device connected to receive current from the secondary circuit of said transformer, and a rectifier in" the in a secondary circuit of said transformer,

a source of alternating current connected to and a gas ionization rectifier connected in said prlmary circuit to unmterruptedly conduct current during useful half wave intervals when said X-ray tube conducts current.

and to prevent current flow during the inverse intervals when said X-ray tube is nonconductive. p V

4. The method of reducing undesired inverse voltages in a rectifying load device connected to a transformer which consists in supplying current continuously to a primary circuit of said transformer during operative intervals of said load device and introducing hereunto set supply a primary circuit of said transformer, V

sufliciently high impedance in said primary 7 t :ircuit during the opposite intervals of no cur-v 7 rent flow in said device to suppress the flow of current in said primary circuit.

5. An X-ray system comprising an electric ary circuit, an X-raytube connected to said secondary c1rcu1t of said transformer, a ther- -m1onic rectifier connected series with the primary circult of said transformer to uninterruptedly transmit current during half wave intervals when said X-ray tube isop- 

